A plasmon is a quantum of plasma oscillation. The plasmon is a quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and mechanical vibrations, respectively. Thus, plasmons are collective oscillations of the free electron gas density, for example, at optical frequencies. Plasmons can couple with a photon to create another quasiparticle called a plasma polariton. Since plasmons are the quantization of classical plasma oscillations, many of their properties can be derived directly from Maxwell's equations.
Surface plasmons are those plasmons that are confined to surfaces and that interact strongly with light resulting in a polariton. They occur, for example, at the interface of a vacuum or material with a positive dielectric constant, and a negative dielectric constant (e.g., a metal or doped dielectric).
The excitation of surface plasmons by light is referred to as a surface plasmon resonance for planar surfaces or localized surface plasmon resonance for nanometer-sized structures. A surface plasmon resonance may influence the spectral characteristics (e.g., absorbance, reflectance, or emittance) of a material.
Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.